Add hidden --preview / --no-preview options to ruff check (#7009)

Per discussion at https://github.com/astral-sh/ruff/discussions/6998

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Adds a `--preview` and `--no-preview` option to the CLI for `ruff check`
and corresponding settings. The CLI options are hidden for now.

Available in the settings as `preview = true` or `preview = false`.

Does not include environment variable configuration, although we may add
it in the future.

## Test Plan

<!-- How was it tested? -->

`cargo build`

Future work will build on this setting, such as toggling the mode during
a test.

crates/ruff_workspace/src/options.rs

@@ -482,6 +482,17 @@ pub struct Options {
     /// field (e.g., `requires-python = ">=3.8"`). If Ruff is configured via
     /// `ruff.toml` or `.ruff.toml`, no such inference will be performed.
     pub target_version: Option<PythonVersion>,
+    #[option(
+        default = "false",
+        value_type = "bool",
+        example = r#"
+            # Enable preview features
+            preview = true
+        "#
+    )]
+    /// Whether to enable preview mode. When preview mode is enabled, Ruff will
+    /// use unstable rules and fixes.
+    pub preview: Option<bool>,
     #[option(
         default = r#"["TODO", "FIXME", "XXX"]"#,
         value_type = "list[str]",